King of the Planets The most massive planet in our solar system -- with dozens of moons and an enormous magnetic field -- Jupiter forms a kind of miniature solar system. It resembles a star in composition, but did not grow big enough to ignite. The planet's swirling cloud stripes are punctuated by massive storms such as the Great Red Spot, which has raged for hundreds of years.

Earth
Our home planet, third from the sun. Earth is the only planet in our solar system not named for an ancient god. In the image on the right, this is the view Apollo 8 astronauts had of Earth while orbiting the moon.More on Earth >>

eccentricity

The eccentricity of an ellipse (planetary orbit) is the ratio of the distance between the foci and the major axis.In other words, the more flattened the circle (ellipse), the more 'eccentric' the orbit. Pluto has a highly eccentric orbit around the sun.

ecliptic

The apparent path of the Sun around the sky.

effusive eruption

a relative quiet volcanic eruption which puts out basaltic lava that moves at about the speed one walks; the lava is fluid in nature; the eruptions at the Kilauea volcano on the island of Hawaii are effusive.

ejecta

The material thrown from an impact crater during its formation.

ellipse

A flattened circle or oval. That the orbits of the planets are ellipses, not circles, was first discovered by Johannes Kepler based on the careful observations by Tycho Brahe. An ellipse is essentially a circle that has been stretched out of shape. When describing ellipses, the eccentricity defines how "stretched out" it is. In the case of the moon (diagram), when it is closest it is at perigee and when it is farthest from Earth is is at apogee.

erosion

The process of physically removing weathered materials; the wearing away of soil and rock by weathering, mass wasting, and the action of streams, glaciers, waves, wind and groundwater.

Earth
Our home planet, third from the sun. Earth is the only planet in our solar system not named for an ancient god. In the image on the right, this is the view Apollo 8 astronauts had of Earth while orbiting the moon.More on Earth >>

eccentricity

The eccentricity of an ellipse (planetary orbit) is the ratio of the distance between the foci and the major axis.In other words, the more flattened the circle (ellipse), the more 'eccentric' the orbit. Pluto has a highly eccentric orbit around the sun.

ecliptic

The apparent path of the Sun around the sky.

effusive eruption

a relative quiet volcanic eruption which puts out basaltic lava that moves at about the speed one walks; the lava is fluid in nature; the eruptions at the Kilauea volcano on the island of Hawaii are effusive.

ejecta

The material thrown from an impact crater during its formation.

ellipse

A flattened circle or oval. That the orbits of the planets are ellipses, not circles, was first discovered by Johannes Kepler based on the careful observations by Tycho Brahe. An ellipse is essentially a circle that has been stretched out of shape. When describing ellipses, the eccentricity defines how "stretched out" it is. In the case of the moon (diagram), when it is closest it is at perigee and when it is farthest from Earth is is at apogee.

erosion

The process of physically removing weathered materials; the wearing away of soil and rock by weathering, mass wasting, and the action of streams, glaciers, waves, wind and groundwater.